1. Field of the Invention
The invention is directed generally to a timing loop based on analog to digital converter output and method of use that provides better timing and/or timing recovery, and more particularly, to a timing loop based on analog to digital converter output and method of use for timing and/or timing recovery that is particularly advantageous for use with optical storage devices.
2. Related Art
In order to generate a timing signal and/or timing recovery signal, such as a read channel clock for the read channel of an optical storage device, conventional Phase Detector (PD) uses the output of a filter arranged downstream of the ADC output, such as a finite impulse response (FIR) filter, as a basis for the generation of the timing signal. Such an arrangement produces inferior performance because the output of the filter, which is used to provide signal equalization to the output of the ADC, causes the timing signal to be compromised. In particular, the filter causes a phase shift in the timing and/or timing recovery signal. This is based, in part, on the fact that the filter is designed predominantly to be adaptive to the density variation of the optical storage device and to focus offsets or other errors of the device or media that require a change in the equalization and the like. Moreover, the filter is designed with a partial response target to improve the performance of a detector circuit such as a Viterbi circuit. Thus, these two design criteria drive the timing signal to have a change in phase as noted above. Accordingly, it is difficult to design a filter, such as a FIR filter, that is well constrained to meet multiple diverse demands.
Additionally, the use of ADCs to read an optical storage device, such as a CD, DVD, HD DVD or Blu-Ray disc, also suffers from manufacturing defects common with the stamping process in the manufacture thereof, or writing of recordable media. Such defects include, for example, variations in pit size and the like. These defects may result in high and low amplitudes that are not equal. The defects may also cause the transitions between land and pit to be shifted. In particular, non-linearity defects cause a deterioration of the performance of the timing loop in the optical storage devices.
Accordingly, it would be desirable to provide an improved timing and/or timing recovery circuit, which is particularly suited for use with optical storage devices.